Hundreds of civil rights lawyers from across America are descending on Ferguson, Missouri as police and protesters prepare for a grand jury decision on whether to charge the officer who killed an unarmed black teenager in August.

The attorneys are arriving in Ferguson as talks between protest groups and police have stalled over a refusal by officials to rule out the use of riot gear, tear gas and militarized equipment if demonstrations turn violent should a grand jury decide not to indict police officer Darren Wilson, protest leaders say.